The invention relates to a pneumatically threadable yarn brake having a substantially tubular brake housing in which a substantially capsular brake cartridge abuts against a lower and an upper brake surface ring, the lower of which brake surface rings is axially displaceable downwardly against a restoring force by the action of a vacuum for the purpose of venting the yarn brake, the brake cartridge having an associated holding device which retains the brake cartridge in an intermediate position with spacing between the upper and lower brake surface rings when the lower brake surface ring is displaced downwardly.
In yarn brakes of this kind described in British patent specification Nos. 2024878A and 20446314A, the lower brake surface ring is fitted centrally in a piston which is axially displaceable within the brake housing and which, for the purpose of releasing the yarn brake, is displaceable downwardly under the action of the vacuum produced by, for example, a yarn threading device in the manner of an injector. In an arrangement of this kind, difficulties can arise with respect to guiding the piston within the brake housing, since, on the one hand, specific sealing between the periphery of the piston and the brake housing is required in order to produce an adequate vacuum, whilst, on the other hand, dust, fiber fly, residues of yarn, brightening agent sprayed from the yarn, and wetting agent can lead to impairment or obstruction of the movement between the piston and the cylinder wall formed by the brake housing. The difficulties arising in this connection, can, of course, be avoided.
An objective of the invention is to design a yarn brake releasable by vacuum, such that the axial displacement of the lower brake surface ring is not impaired by contamination of the above-mentioned kind occurring within the brake housing.
A pneumatically threadable yarn brake in accordance with the invention has a substantially tubular brake housing in which a brake cartridge abuts against a lower and an upper brake surface ring, the lower of which brake surface rings is axially displaceable downwardly against a restoring force for the purpose of releasing the yarn brake cartridge having an associated holding device which retains the brake cartridge in an intermediate position with spacing between the upper and lower brake surface rings when the lower brake surface ring is displaced downwardly, the lower brake surface ring being secured to an annular diaphragm whose outer periphery is fixedly clampable and which defines the top of a chamber connectible to a source of vacuum for the purpose of displacing the diaphragm against the restoring force.
Any contamination which occurs does not affect the movement of this annular diaphragm, since, in contrast to the above-mentioned piston and cylinder combination, there is now no need for sealing surfaces which move or slide relative to one another.